"It's said the swelling of their minds cast deep shadows over their vision; such that most only ever looked down, and when they did look up, could see nothing but their own genius." - The Annals of Orymir

I won't loredump here since I'm so far behind (check me out on DA if you just really wanna read my worldbuilding notes) but the long and short of these guys is that they're basically an ancient society who discovered and mastered an art which they called "Life Control." They first used it to modify other creatures and their own bodies, but after reaching the limits of what they could do, decided to enhance their own brains with it. This lead to a downwards spiral of further and further modification, where their ambition, darkness of thought, and infatuation with strange and grotesque things quickly snowballed out of control. The result was a monster-infested world, so desolate and so overrun with such immense and horrific creatures, that it resembled something like artificial cosmic horror.

The Magites were eventually whittled down to near extinction by their own perverse creations, before both were sealed away by a coalition of their strongest rivals in a desperate war.